public void Test_GetApproxArea_LargeShellAndHolePolygon()
{
// Make sure that GetApproxArea works well for large polygons.
Assert2.Near(S2.GetApproxArea(MakeLaxPolygonOrDie(
"0:0, 0:90, 90:0; 0:22.5, 90:0, 0:67.5")),
S2.M_PI_4, 1e-12);
}
// Like GetArea(), except that this method is faster and has more error. The
// additional error is at most 2.22e-15 steradians per vertex, which works out
// to about 0.09 square meters per vertex on the Earth's surface. For
// example, a loop with 100 vertices has a maximum error of about 9 square
// meters. (The actual error is typically much smaller than this.)
public static double GetApproxArea(S2ShapeIndex index)
{
double area = 0;
for (int i = 0; i < index.NumShapeIds(); ++i)
{
var shape = index.Shape(i);
if (shape != null)
{
area += S2.GetApproxArea(shape);
}
}
return(area);
}
// Like GetArea(), except that this method is faster and has more error. The
// additional error is at most 2.22e-15 steradians per vertex, which works out
// to about 0.09 square meters per vertex on the Earth's surface. For
// example, a loop with 100 vertices has a maximum error of about 9 square
// meters. (The actual error is typically much smaller than this.)
public static double GetApproxArea(S2Shape shape)
{
if (shape.Dimension() != 2)
{
return(0.0);
}
double area = 0;
int num_chains = shape.NumChains();
for (int chain_id = 0; chain_id < num_chains; ++chain_id)
{
GetChainVertices(shape, chain_id, out var vertices);
area += S2.GetApproxArea(vertices.ToList()); //todo
}
// Special case to ensure that full polygons are handled correctly.
if (area <= S2.M_4_PI)
{
return(area);
}
return(area % S2.M_4_PI);
}